The present invention relates to semiconductor devices using a lead frame for a resin-sealed package which is used in a microwave band, and more particularly to semiconductor devices that are applicable to power amplifiers.
Devices capable of implementing both high performance and low cost have been desired for microwave high-output power amplifiers. Transistors that are used for high-output power amplifiers typically tend to have lower high-frequency input/output impedance in the case of field effect transistors (FETs) because the gate width is increased. The actual resistance value is at most 2Ω to 3 Ω.
As the standard impedance is 50Ω in a high frequency circuit section in a set such as communication equipment etc., input/output terminals of the high-output power amplifier need be matched to 50Ω. In the case of converting the low impedance at the input/output terminals of the transistor to 50Ω, high frequency loss due to the low impedance is not caused
FIG. 32A shows on a Smith chart an impedance conversion path and constituent elements that are used to attain 50Ω matching from an input impedance point of the transistor. By using the input impedance point of the transistor as a starting point, a series inductor element and a parallel capacitor element are sequentially connected in this order, and the impedance value of each element is appropriately selected, whereby the impedance can be converted to 50Ω. However, as shown in FIG. 32B, if the inductance value is too large or the capacitance value is too small or too large, the impedance is separated from the predetermined point of 50Ω, resulting in an impedance mismatch state.
As shown in FIG. 33A, a bonding wire 3 is typically used to connect a semiconductor chip including a transistor 1 to a lead 2 in a package 10. The lead 2 and the bonding wire 3 are represented by an equivalent circuit formed by a series inductance component and a parallel capacitance component. In this case, matching circuits 11 are provided on a board outside the package 10 so as to attain 50Ω input/output impedance matching.
As described above, if the transistor 1 has low input/output impedance, high frequency loss of the wire 3 itself becomes non-negligible as the wire 3 becomes longer. Such high frequency loss causes reduction in gain. As shown in FIG. 33B, in order to achieve 50Ω matching, a pre-matching circuit 5 having a pre-matching function is usually connected near the input/output terminal of the transistor 1 in order to increase an actual resistance component of the impedance. The pre-matching circuit 5 suppresses as much as possible the power loss that is caused by conversion of the impedance to high impedance. The pre-matching circuit 5 uses a configuration of a monolithic microwave integrated circuit (MMIC) in which the pre-matching circuit 5 is monolithically formed on the semiconductor chip where the transistor 1 is formed, or a hybrid configuration in which the pre-matching circuit 5 is formed on a separate semiconductor chip and is connected by a wire.
In terms of the manufacturing cost, it is desirable that high performance can be attained without using the MMIC and the hybrid composition.
Ceramic packages are typically used as packages for high-output power amplifiers. The ceramic packages are expensive although they have excellent high-frequency characteristics and heat dissipation characteristics. In order to reduce the cost, it is preferable to use resin-sealed packages it is acceptable in terms of their heat dissipation characteristics including heat resistance, although the resin-sealed packages are subjected to limitation by the specification such as the output power level and efficiency of the high-output power amplifier.
Semiconductor devices according to first and second conventional examples will be described with reference to FIGS. 34A and 34B (see, e.g., Japanese Translation of PCT International Application No. 2008-541435 (FIGS. 2 and 3) and U.S. Pat. No. 7,375,424 (FIGS. 2 and 3)).
As shown in FIG. 34A, the semiconductor device according to the first conventional example has a lead frame 102 having a die pad 104 and a plurality of terminal leads 110 to 118, and a device 101 fixed to the die pad 104. Bond pads 110a to 118a provided at the ends of the terminal leads 110 to 118 are arranged so as to adjoin the lower end of the die pad 104 and to cross the bottom of a device package. A source electrode 23, a drain electrode 22, and a gate electrode 20 of the device 101 are electrically connected to the terminal leads through a plurality of wire bonds 120, 121, etc. extending from a runner of each electrode to the bond pads 110a, 112a, etc.
As shown in FIG. 34B, the semiconductor device according to the second conventional example has a lead frame 202 having a die pad 204 and a plurality of terminal leads 210 to 214, and a device 201 fixed to the die pad 204. The bond pads 210a, 214a connected to elongated power electrodes 25, 26 of the device 201 by wire bonds 220, 222, etc. are arranged so as to extend adjacent to the opposing peripheral edges (side surfaces) of the die pad 204. That is, the bond pads 210a, 214a are arranged so as to extend parallel to the longitudinal direction of the power electrodes 25, 26 of the device 201 and adjacent to the power electrodes 25, 26 of the device 201.
With this configuration, the plurality of wire bonds 220 connecting the first power electrode 25 to the bond pad 210a and the plurality of wire bonds 222 connecting the second power electrode 26 to the bond pad 214a are arranged substantially parallel to each other and with substantially the same length along the power electrodes 25, 26 and the bond pads 210a, 214a. 
A semiconductor device according to a third conventional example will be described with reference to FIGS. 35A-35C (see, e.g., Japanese Patent Publication No. 2004-119610 (FIG. 10)).
As shown in FIGS. 35A-35C, a lead frame includes a die pad portion 11 and a heat dissipation plate 12 which are formed by a thin plate portion, and a frame portion, a suspension lead portion 14, an external connection lead portion 15, and a tie bar portion which are formed by a thin plate portion. The suspension lead portion 14 is connected to an upper part of the die pad portion 11, and the end on the die pad portion 14 side of the suspension lead portion 14 is bent in a beak shape to form a heat conduction region 14b as a region where a part of the upper surface of the suspension lead portion 14 is located above the die pad portion 11.
The bent portion including the heat transmission portion 14b is bent such that the frame portion side of the suspension lead portion 14 is located above the upper surface of the die pad portion 11 and extends in a direction parallel to the upper surface of the die pad portion 11. This reduces the distance between the die pad portion 11 and the frame portion, and the external connection lead portion 15 connected to the suspension lead portion 14 by the frame portion and the tie bar portion has an overhang structure in which the end on the die pad portion 11 side of the external connection lead portion 15 overhangs the die pad portion 11. As a result, the end on the die pad portion 11 side of the external connection lead portion 15 serves as an inner lead portion 15a connected to a semiconductor chip 21, and the end on the frame side of the external connection lead portion 15 serves as an outer lead portion 15b connected to a mount substrate.
Since the end on the die pad portion 11 side of the external connection lead portion 15 overhangs the die pad portion 11, the distance to the semiconductor chip 21 can be reduced.
The semiconductor chip 21 is fixed to the upper surface of the die pad portion 11, and as shown in FIG. 35C, a plurality of element electrodes (not shown) of the semiconductor chip 21 are connected to the inner lead portion 15a via metal thin wires 22.
As shown in FIG. 35B, the suspension lead portion 14 is connected to the semiconductor chip 21 via a metal thin wire 22, so that a ground potential is supplied to the semiconductor chip 21.
The die pad portion 11 and the semiconductor chip 21 are integrally sealed by a resin sealing portion 23.